From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 836D6DDD2; Thu, 16 Oct 2025 04:40:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.95.11.211 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760589605; cv=none; b=uY90msAiFXSsZ3AOTvWID1gfYKTKmfI6wku6j/OcWUP2bBb3a3yIb1adF0U9XayN9etYrq/spz/xu6OWr1Rtfi8SYc5AJAjB3HzcuVN8trvYfpAkJrlR8oNcLOIm2BJ70QCbPMzG/7vHi8bOljDAj0N2vTEQC5vsAo62azmMeFs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760589605; c=relaxed/simple; bh=B2dmelacR9KDdjcvdVHbE8VVaP1pY5MFfMjNVGaoa18=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=K6iTeTtvGXYOvJhArYWTsw3va4ByvnDw+R6crBGJFviBelDi8FAHW+9OHw5G0DMQ+fM/7IQxq1tTl9Tl/VYlG6pYrCvBC0u+/A4TlSEpMtQXVfJVqDN4sNh0fKdycqglIPWbiMTSphetV+/VPlv/LFLj6OtnaNc7+liUvdepHdg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de; spf=pass smtp.mailfrom=lst.de; arc=none smtp.client-ip=213.95.11.211 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=lst.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 66F11227A87; Thu, 16 Oct 2025 06:39:59 +0200 (CEST) Date: Thu, 16 Oct 2025 06:39:58 +0200 From: Christoph Hellwig To: Dave Chinner Cc: Christoph Hellwig , Christian Brauner , Jan Kara , Carlos Maiolino , Andrew Morton , willy@infradead.org, dlemoal@kernel.org, hans.holmberg@wdc.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH 2/3] writeback: allow the file system to override MIN_WRITEBACK_PAGES Message-ID: <20251016043958.GC29905@lst.de> References: <20251015062728.60104-1-hch@lst.de> <20251015062728.60104-3-hch@lst.de> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) On Thu, Oct 16, 2025 at 07:49:20AM +1100, Dave Chinner wrote: > On Wed, Oct 15, 2025 at 03:27:15PM +0900, Christoph Hellwig wrote: > > The relatively low minimal writeback size of 4MiB leads means that > > written back inodes on rotational media are switched a lot. Besides > > introducing additional seeks, this also can lead to extreme file > > fragmentation on zoned devices when a lot of files are cached relative > > to the available writeback bandwidth. > > > > Add a superblock field that allows the file system to override the > > default size. > > Hmmm - won't changing this for the zoned rtdev also change behaviour > for writeback on the data device? i.e. upping the minimum for the > normal data device on XFS will mean writeback bandwidth sharing is a > lot less "fair" and higher latency when we have a mix of different > file sizes than it currently is... In theory it is. In practice with a zoned file system the main device is: a) typically only used for metadata b) a fast SSD when not actually on the same device So I think these concerns are valid, but not really worth replacing the simple superblock field with a method to query the value. But I'll write a comment documenting these assumptions as that is useful for future readers of the code. > > -Dave. > -- > Dave Chinner > david@fromorbit.com ---end quoted text---